1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, it relates to technique of preventing thermal breakdown following a temperature rise in a power device.
2. Description of the Related Art
In a power device employed for high power use, a temperature protection network is generally utilized in order to prevent thermal breakdown following an excess temperature rise. FIG. 20 shows an example of such a conventional temperature protection network. As shown in FIG. 20, a power device 1 is formed by an enhancement type n-channel field effect transistor and a diode 3 connected in parallel between a source and a drain of the field effect transistor 2. The source of the field effect transistor 2 is grounded and the drain thereof is connected to a DC power supply V.sub.DC through a load 4. A control signal IN is inputted in the gate of the transistor 2 through a driver 5, to thereby perform voltage control of the power device 1. In this case, the power device 1 is controlled by an on-off control system employing a binary level signal as the control signal IN or a pulse width modulation control system employing a pulse shape signal. On the other hand, a temperature sensor 6 such as a thermocouple is separately provided in the vicinity of the power device 1, in order to detect the temperature of the power device. A temperature measuring signal, having a voltage value relating to a measuring temperature outputted from the temperature sensor 6, is inputted in an error amplifier 7. The error amplifier 7 compares a temperature detecting signal received from the temperature sensor 6 with reference voltage 8, to output an abnormal temperature detecting signal when the temperature of the power device 71 rises to a prescribed abnormal temperature level to supply the abnormal temperature detecting signal to another input terminal of the driver 5.
Operation of the temperature protection network thus structured is as follows: When the power device is in a normal temperature range, the error amplifier outputs no abnormal temperature detecting signal, and hence the control signal IN directly passes through the driver 5 to be supplied to the gate of the transistor 2, thereby to continue operation by the power device 1. When the temperature of the power device 1 exothermically rises to the prescribed abnormal temperature level, the abnormal temperature is detected by the temperature sensor 6 so that the error amplifier 7 outputs the abnormal temperature detecting signal to the driver 5. Upon receiving the abnormal temperature detecting signal, the driver 5 switches the output voltage level of the driver 5 from "H" to "L" in case of the on-off control system, for example, to turn off the power device 1. In the case of the pulse width modulation control system, on the other hand, the driver 5 modulates the pulse width of the output of the driver 5 to lower the output of the power device 1. Thus, the temperature of the power device 1 is lowered to prevent thermal breakdown. The diode 3 of the power device is adapted to bypass a current flowing in the power device 1 by counter-electromotive force of the inductive load 4 when the transistor 2 is turned off.
In the conventional temperature protection network for a power device. However, the temperature sensor 6 such as a thermocouple is separately provided exterior to the power device as hereinabove described, whereby the device is enlarged in size to increase the cost. Further, an error between the measuring temperature of the temperature sensor 6 and the actual temperature of the power device 1 is largely dispersed depending on conditions such as heat sink and the mounting position of the temperature sensor 6, to thereby decrease the reliability of the prevention of thermal breakdown of the power device 1.